Over the course of five election seasons between 2000 and 2004, researchers from Princeton University showed potential voters photographs of political candidates running in a slew of U.S. congressional races.

The voters were told nothing about the candidates, who were running for seats in both the U.S. Senate and House of Representatives.

Researchers tested voters' snap judgments about the political candidates. Attractiveness, honesty, and likeability were just some of the traits measured, but the one that stood out for voters was a candidate's competence.

Voters' competence ratings were based solely on the appearance of a candidate's face and predicted the outcomes in U.S. congressional races over five election seasons at a rate of nearly 70 percent.

"We didn't have a firm hypothesis that competence would drive [results]," said Princeton psychologist Alexander Todorov. "It was surprising that the inference was very specific to what people consider important in a politicianand they say that's competence."

Snap decision-making processes like those examined in the study are not necessarily conscious, Todorov said.

"We do a lot of research on how people form impressions of other people, and from our work, as well as work in other labs, we thought that a lot of inferences from facial appearance are pretty automatic," the psychologist said.

"Even if you don't intend to form impressions of a person, it happens quickly," he added.

Researchers excluded any results in which participating voters recognized a candidate or said a candidate even looked familiar.

That part of the exercise revealed what Todorov describes as a "stunning" level of anonymity for both political challengers and sitting Congressmen.